This invention relates to a gas burner and sealed combustion chamber of a heating appliance such as a hot water heater for providing a low NOx, low CO burner system having a high heat release and permitting manifold pressures which are relatively low, the system providing increased efficiency and having no exposed flame.
Gas water heaters, for example, typically comprise a cylindrical tank having a concentric inner cylinder of smaller diameter acting as a flue for the combustion products for transfer of heat from the products of combustion to the water which is disposed between the cylinders. This transfer of heat takes place throughout the length of the inner cylinder and at the top of the generally semi-spherical top of the combustion chamber. Most water heaters in the United States use burners which require secondary air and have high NOx (nitrite oxide and nitrogen dioxide) outputs. In attempts to reduce the output of NOx in these appliances prior art burners in the United States have been of the thermally active type, i.e., they comprise a large mass of metal that reduces the temperature of the flame as it heats up and acts as a heat sink from the flame. This reduction in flame temperature results in consequential reduction of NOx. One of the difficulties with these burners is that they only reduce NOx for a short period of time--while they are thermally active. Once these burners have become hot, the NOx levels are typically of a partially aerated burner, e.g. 50% primary air and 50% air disposed about the burner, and therefore the NOx levels are unacceptably high. It may be noted that the formation of NOx (both NO and NO.sub.2) is undesirable since it contributes to acid rain and the formation of smog. California, for example, has imposed restrictions on the amount of NOx emissions from residential water heaters and other appliances.
Moreover, because of the requirement for secondary air in the burners used in water heaters of the prior art, there are air openings in the water heater which exposes the flame. This may have resulted in numerous cases of physical damage to human beings and property when flammable vapors have leaked to the vicinity of the water heater and ignited. When gasoline, flammable paint, paint thinners or the like are located in the same room or garage as the water heater, if these flammable materials should spill, ignition of the vapor and its source has been reported to occur on a number of occasions.
Other burners, such as that disclosed in PCT International Publication No. WO-92/01196, used primarily in boilers in Europe require higher manifold pressures in the order of approximately six to seven inches of water, and in the case of the burners illustrated in the aforesaid PCT application, 40 to 180 inches of water. In any event, prior art burners have not operated with manifold pressures as low as four inches of water as is typically available in the United States. The port loading, i.e., heat release per unit of area, is relatively low with prior art burners.